MITOTIC PERTURBATION AND G2 CELL CHROMATID ABERRATIONS .5.

There is no cell system in current usage that has a uniform radiosensi tivity for the production of chromatid-type aberrations. Consequently, aberration frequencies fluCtuate with sample-time after exposure; the re is no unique yield to set against absorbed dose. Given this situati on, the observed yields, and their time-profiles, are subject to modif ication by cell kinetic factors, in particular, the mitotic delay whic h inevitably accompanies all clastogenic treatments. This paper discus ses some cell-cycle modelling methods which attempt to explore the eff ects of these perturbations on aberration frequencies, and which, in t ime, may alloW us to correct observed yields to obtain reliable, and u seable, scores of chromatid structural changes.